实体框架“发生关系多重约束违反”。 [英] Entity Framework "A relationship multiplicity constraint violation occurred"

问题描述

我今天早上从Entity Framework收到此错误：

I received this error from Entity Framework this morning:

发生了一种关系多重约束，即：EntityReference不能有多个相关对象，但是该查询返回了多个相关对象。这是不可恢复的错误。

该错误是指 User之间的非常简单的一对多关系和地址

public class User
{
    public Guid Id { get; set; }
    public virtual IList<Address> Addresses { get; set; }
} 

public class Address
{
    public Guid Id { get; set; }
    public User User { get; set; }
} 

我正在使用Fluent API配置实体之间的关系，但是在在这种情况下，这种关系似乎很简单，首先我没有指定任何特定规则，而是让EF推论该关系：

I'm using Fluent API to configure the relationship between entities, but in this case the relationship seems to simple that at first I didn't specify any particular rule and I let EF "deduce" the relationship:

public class AddressConfiguration : EntityTypeConfiguration<Address>
{
    public AddressConfiguration()
    {
        HasKey(a => a.Id);
        Property(a => a.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity).IsRequired();
    }
}

public class UserConfiguration : EntityTypeConfiguration<User>
{
    public UserConfiguration()
    {
        HasKey(u => u.Id);
        Property(u => u.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity).IsRequired();
    }
}

但是收到错误后，我尝试指定以下内容AddressConfiguration中的规则：

But after receiving the error I tried to specify the following rule in the AddressConfiguration:

public class AddressConfiguration : EntityTypeConfiguration<Address>
{
    public AddressConfiguration()
    {
        HasKey(a => a.Id);
        Property(a => a.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity).IsRequired();
        HasOptional(x => x.User).WithMany(); // I tried adding this
    }
}

尝试生成一个新的自动迁移，这是我获得的：

After doing that, I tried generating a new automatic migration, and this is what I obtained:

public partial class AddressFixMigration : DbMigration
{
    public override void Up()
    {
        DropForeignKey("dbo.Addresses", "User_Id", "dbo.Users");
        AddColumn("dbo.Addresses", "User_Id1", c => c.Guid());
        CreateIndex("dbo.Addresses", "User_Id1");
        AddForeignKey("dbo.Addresses", "User_Id1", "dbo.Users", "Id");
    }

    public override void Down()
    {
        DropForeignKey("dbo.Addresses", "User_Id1", "dbo.Users");
        DropIndex("dbo.Addresses", new[] { "User_Id1" });
        DropColumn("dbo.Addresses", "User_Id1");
        AddForeignKey("dbo.Addresses", "User_Id", "dbo.Users", "Id");
    }
}

我发现这很奇怪。在地址表具有外键 User_Id的情况下，Db似乎还可以，但是在配置文件中指定了一对多关系后，EF想要创建一个不同外键。为什么？

I found this very odd. The Db seemed ok even before, with the Addresses Table having a Foreign Key "User_Id", but after specifying the one-to-many relationship in the Configuration file EF wants to create a different Foreign Key. Why??

我还尝试指定 HasOptional（x => x.User）.WithMany（）。Map（x => x.MapKey（ User_Id））; ，但是在那种情况下，当我尝试创建自动迁移时，会收到以下错误：

I also tried to specify HasOptional(x => x.User).WithMany().Map(x => x.MapKey("User_Id"));, but in that case when I try to create the automatic migration I receive the following error:

User_Id：名称：类型中的每个属性名称都必须是唯一的。属性名称'User_Id'已经定义。

我的数据库似乎显然有问题，但是我看不到什么以及为什么。

It seems like something is clearly wrong with my DB, but I can't see what and why.

推荐答案

我意识到我需要更改配置文件，如下所示：

I realized that I needed to change my Configuration file as it follows:

public class AddressConfiguration : EntityTypeConfiguration<Address>
{
    public AddressConfiguration()
    {
        HasKey(a => a.Id);
        Property(a => a.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity).IsRequired();
        HasOptional(x => x.User).WithMany(x => x.Addresses).Map(x => x.MapKey("User_Id"));
    }
}

.WithMany（）（无参数）用于关系的另一端没有导航属性时，而在这种情况下，我需要将 .WithMany（x => x.Addresses ），因为用户实际上包含地址列表。

.WithMany() (without parameter) is for when there is no navigation property on the other side of the relationship, while in this case I needed to spacify .WithMany(x => x.Addresses) because User actually contains a list of Addresses.

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